Organosilicon compounds may be prepared in general by the addition reaction of unsaturated hydrocarbons with Si—H containing silanes or siloxanes. For example, Walter Noll describes in Chemistry and Technology of Silicones, Second Edition (1968), Pages 49-55, the addition reaction for silanes and siloxanes. This type of addition reaction to hydrocarbons containing carbon-carbon multiple bonds is termed hydrosilylation. Heat, light, radiation, or catalysts may initiate hydrosilylation reactions. Catalysts may be noble metals, bases, or peroxides. Noble metals, especially platinum, are usually preferred. The form of catalyst may be homogeneous or heterogeneous.
Hydrosilylation reactions utilizing unsaturated hydrocarbons that are gaseous at reaction conditions have had reported deficiencies related to incomplete reactions, slow batch reaction rates to avoid loss of the hydrocarbon, and formation of secondary (disilylalkane) byproducts in the case of alkenylsilanes, wherein the disilylalkanes correspond to the primary alkenylsilane products.
For example, U.S. Pat. No. 3,404,169 discloses the preparation of vinylhalosilanes by the reaction of acetylene with a halo-hydrogensilane at atmospheric pressure and moderate temperature in a liquid aromatic diluent in the presence of a platinum catalyst. The '169 patent discloses that reactants are introduced in a premixed form through a single tube, which dips to the bottom of the reactor and ends in a sintered glass cylinder having pores. In apparent recognition of poor mixing at the tube exit, the '169 patent discloses that an agitating device may be advantageous to homogenize the reaction mass and avoid local over-heating. Reported patent example product selectivity calculated on the amount of feed silane consumed were 83%, 86% and 91% for three examples of methylvinyldichlorosilane preparation, 81% for dimethylvinylchlorosilane, and 87% and 91% for vinyltrichlorosilane. The yield losses were predominantly to disilylethane byproducts.
U.S. Pat. No. 3,793,358 discloses that an alkenylsilane may be prepared by reacting acetylene or substituted acetylene with a silane having at least one silicon bonded hydrogen atom in the presence of an addition catalyst and disilylethane at a temperature from about 120° C. to about 220° C. at a pressure from about 0.1 to about 5 atmospheres gauge, and the resulting alkenylsilane is removed continuously as a gas from the reaction space at the rate at which it is formed. Examples of the '358 patent provide that reactants are introduced at 0.4 atmospheres gauge pressure in a premixed form below a perforated plate into the lower end of a reaction tower containing disilylalkane and platinum catalyst. This pressure is generally considered a safe condition for the use of acetylene. Acetylene decomposition is known to occur at pressures above 15 psig or approximately 1 atmosphere gauge. No additional mixing in the reaction tower is disclosed. In the Examples of the '358 patent, product selectivity calculated on the amount of feed silane consumed were 87% and 88% for methylvinyldichlorosilane, 92% and 95% for vinyltrichlorosilane, and a reported 74% product concentration for dimethylvinylchlorosilane. The yield losses were predominantly to disilylethane byproducts.
U.S. Pat. No. 4,276,426 discloses a process for preparing organosilicon compounds by the continuous introduction of a halosilane, dihalosilane, or disiloxane having Si-bonded hydrogen, a compound containing an aliphatic multiple bond, and a catalyst to a pipe shaped reactor, where the reaction mixture is maintained in a liquid phase and is being continuously removed from the reactor, wherein the reaction mixture is circulated in the reactor at a rate of at least 1,000 cm per minute. According to the patent examples, the reaction is conducted from about 120° C. to about 170° C. at a pressure of approximately 6 bar. Although this pressure is above the “safe” pressure for acetylene, the reactor inside diameter is limited to 20 mm, which is less than the detonation propagation limit. Unless many such pipe reactors are combined into a complex multi-pipe unit, this reactor diameter limit severely restricts the production capacity that could be obtained and hence it is not commercially practical.
U.S. Pat. No. 4,579,965 discloses the preparation of vinyl tri(tertiary-substituted) alkoxysilanes by reacting a tri-t-alkoxysilane with an alkyne in the presence of a platinum hydrosilylation catalyst at a reaction temperature greater than 150° C. The reaction is conducted at the alkenyl gas inlet pressure, which is greater than atmospheric. The reaction is conducted in an autoclave with a batch time from about 1 to 3 hours with a large excess of acetylene. Product selectivity was reported to be greater than 90% for tertiary alkoxysilane. For primary and secondary alkoxysilanes, the selectivity was poor. Therefore the process of the '965 patent has a narrow practical application, as most vinylsilanes of commercial interest are primary silanes.
U.S. Pat. No. 4,898,961 discloses the continuous preparation of alkenylsilanes whereby a gaseous mixture of acetylenic hydrocarbon and a silane containing a silicon-bonded hydrogen atom is directed into contact with a reaction medium containing a hydrosilylation catalyst and in the form of a thin liquid layer or film. According to the '961 patent, the reaction medium is preferably the product of the reaction or can optionally be a solvent, and the reaction is conducted below the decomposition pressure of the acetylenic hydrocarbon (less than 2 atmospheres) and in the temperature range of 50° C. to 80° C. The form of the reactor is a vertical tube reactor wherein the liquid medium flows as a layer or film within the tubes and the exterior of the tubes is water-cooled. The liquid reaction medium is introduced to the upper end of the tubes through a distributor weir to direct the flow along the tube walls. The gaseous mixture is introduced through nozzles to the bottom of the tubes. The '961 patent examples disclose the effect of using a solvent that has greater solubility for acetylene and reports that dimethyl ether of ethylene glycol is more effective than methylethyl ketone, which in turn is more effective than xylene.
Product selectivity for methylvinyldichlorosilane ranged from about 93% when using xylene to about 95% when using dimethyl ether of ethylene glycol. U.S. Pat. No. 5,041,595 discloses a batch or continuous method for producing high purity vinylalkoxysilanes by gradually feeding an alkoxysilane containing low levels of ionic chloride or alkyl amine into a reaction zone containing an alkyne and a platinum hydrosilylation catalyst. The '595 patent discloses that the total concentration of ionic chloride and alkyl amines (measured as nitrogen) contaminants is maintained below 0.1 weight percent and most preferably below 0.005 weight percent, which minimizes the formation of tetraalkoxysilane and alkylalkoxysilane byproducts. The reaction zone is operated at less than 75 psia and preferably less than 25 psia and at a temperature between about 50° C. and about 150° C. The reaction medium is vinylalkoxysilane product or disilylalkoxyalkane or a solvent selected from cumene, toluene, xylene, and o-dichlorobenzene and may optionally contain a reaction promoter selected from the group consisting of phenothiazine, diphenylmethane, diphenylamine, and carboxylic acids promoter.
The '595 patent discloses that good mixing is important in the process of the invention. A stirred reactor was used for the patent example experiments. Patent example product selectivity calculated on the amount of feed silane consumed for the preparation of vinyltrimethoxysilane in o-dichlorobenzene solvent were about 92% at atmospheric pressure and about 96% at a pressure of 7-12.7 psig. When the reaction medium was vinyltrimethoxysilane product, the product selectivity was 87% at a reaction pressure of 7 psig and when the reaction medium was disilyltrimethoxyethane, the product selectivity was 89% at atmospheric pressure. Product selectivity for a methylvinyidimethoxysilane preparation example was 96% at 12.3 psig and in o-dichlorobenzene solvent.
U.S. Pat. No. 6,414,176 discloses the preparation of vinylsilanes by reacting silanes with a liquid phase at superatmospheric pressure containing acetylenic hydrocarbon and a hydrosilylation catalyst. The spent actylenic hydrocarbon is replenished during the reaction while maintaining a constant pressure. Silane is added to the liquid phase, which already contains the acetylenic hydrocarbon and catalyst. The effect of maintaining a constant concentration of acetylenic hydrocarbon throughout the reaction is that the reaction is conducted at high molar excess of the acetylenic hydrocarbon. The '176 patent discloses that the reaction is preferably conducted in an inert high boiling solvent, selected from aliphatic and aromatic hydrocarbons, and that high boiling aromatic hydrocarbons are particularly preferred. The '176 patent discloses that the reaction is preferably conducted at a low temperature of from 40° C. to about 50° C. and at a pressure of 15 to 20 bar, which is well above the generally considered safe pressure of 15 psig, the pressure where acetylene decomposition can begin. The reaction yield for vinyltrimethoxysilane was disclosed in an example as 99%.
U.S. Pat. No. 7,005,532 discloses the batch or continuous preparation of organoalkoxysilanes by hydrosilylating an organosilicon compound having at least one hydrogen-silicon bond and at least one alkoxy group and an organic compound having a carbon-carbon unsaturated bond in vapor phase in the presence of a mixture containing a hydrosilylation catalyst and a polyalkylene glycol and supported on an inert carrier. The '532 patent discloses that the process is conducted at a preferred temperature range of 100-180° C. and at a preferred pressure of 1-5 MPa (10-50 Bar), and always less than 10 MPa (100 Bar), which are all well above the generally considered safe pressure of 1 bar gauge, the pressure where acetylene decomposition can occur. Indicated reactor types are vibrating bed, moving bed, fixed bed, or fluidized bed. Product selectivity for vinyltrimethoxysilane was 94%, 94%, and 97% for the three patent examples, but reaction yield was 67%, 51%, and 83% for the same examples because of relatively low conversion of the feed trimethoxysilane. Product selectivity for vinyltrichlorosilane was 85% and reaction yield was 52%.
It would be desirable to devise an improved method for the preparation of organohalosilanes, organoalkoxysilanes, and organosiloxanes from gaseous unsaturated hydrocarbons at high product selectivity and in high conversion yield. It would be also be particularly desirable to prepare dimethylvinylchlorosilane in high yield.